The present invention relates to an integral, low power, high efficiency motor and control particularly suitable for use in applications where high reliability and high efficiency are particularly important, such as, for example, household refrigeration systems.
In conventional refrigerators of the residential or household type a compressor pumps a circulating refrigerant such as freon to a condenser coil where heat is extracted. The condenser coil is typically positioned on the exterior of the refrigerator, and air circulates over and around the condenser coils (with or without assistance from a fan or blower) to extract heat therefrom. The cooled refrigerant is then circulated through an evaporator coil within the refrigerator, typically in a freezer compartment, to cool the space within the refrigerator. The refrigerant then circulates to the compressor and thence back to the condenser. This cycle continues until the temperature within the refrigerator reaches a desired preselected temperature as sensed by a thermostat or temperature control. A small motor driven evaporator fan is normally provided within the freezer compartment to circulate air over the evaporator coils, through the freezer compartment, and between the freezer compartment and the remainder of the refrigerator.
A conventional fan motor is typically a low power motor having a power input in the range of 8.5 to 13.5 watts with an output power of approximately 2.5 watts. Thus, it will be understood that the efficiency of conventional evaporator fan motors is generally in the order of less than 30%. It also should now be understood that 70% or more of the electric power supplied to such motors is converted to heat within the refrigerator (or freezer compartment), and such heat must be removed from the interior of the refrigerator by the refrigeration system. Thus, inefficient evaporator fan motor operation is undesirably leveraged, because each watt of heat released in the freezer increases the cooling and thus power demands on the refrigerant compressor motor and the remainder of the system. Typically, with other things being held constant, the release of one extra watt of heat inside a refrigerator requires in excess of one extra watt of compressor motor power to remove each such watt of heat generated within the refrigerator. Even with a highly efficient refrigeration system it would typically require in excess of 1.2 additional watts of input power to compressor and condenser fan motors compensate for each additional watt of power dissipated by an evaporator fan motor inside the refrigerated compartment. This amounts to a total power leverage factor of 2.2.
One major objective of the present invention is to provide a new and improved motor and control such that the just referred to undesirable leverage can be viewed as desirable, and used to reduce the overall power consumption by a refrigeration system. For example, if one were able to reduce evaporator fan motor input power requirements by an initial 8 watts per hour, then one could reduce the overall refrigerator power requirements by the initial 8 watts plus an additional 7 or more watts (at the compressor and condenser) and this all could amount to as much as 90 kilowatt hours per year, which could represent as much as 10% of the total annual power consumption of a typical household refrigerator.
This power reduction is significant, however, not only in its cost savings to a consumer over the life of a refrigerator, but also in helping to reduce the burning of fossil fuels to generate such power. Moreover, the power savings just mentioned can assist in enabling a refrigerator to meet the power reduction regulations and/or incentives of state and federal governmental bodies.
Public concern about electrical power consumption, is reflected by proposed legislation and U.S. Department of Energy (DOE) regulations, and has emphasized the need to increase the efficiency of household appliances to reduce both the amount of fossil fuel burned, and the need for additional power generation capacity. Public interest and demand is reflected in Energy Guide labels or tags on household appliances which disclose the power requirements and typical cost of operation information.
A still further complication in the redesign of some motors, and particularly refrigerator evaporator fan motors, is the need that the substitute motor fit within the space envelope available in present refrigerator designs, since it would be costly to change existing tooling used in manufacturing refrigerators simply to accommodate differently sized motors. Moreover, it is desirable to utilize a high efficiency motor to replace an existing motor for repair purposes. Thus, it is very desirable that improved motors (and controls when packaged therewith) be usable in existing space envelopes.
In addition there is growing concern over release into the atmosphere of freon refrigerants used in refrigerators and of chemicals used as foaming agents during the manufacture of insulation used in refrigerator walls. Concern over the possible damage to the ozone layer in the earth's atmosphere by CFCs (chlorofluorocarbons) in the refrigerant is leading to the use of alternate refrigerants. However, presently available alternate refrigerants are less efficient than the freon presently used, so their use would further reduce the efficiency of refrigeration systems. Moreover, the foam insulation used in the walls of refrigerators typically utilizes CFCs as the blowing agent during manufacture, while the use of other known substitute materials result in insulations with reduced R factors. This all further increases the desirability of reducing the amount of heat released by a motor inside a refrigerated enclosure.
The need to further increase the efficiency of electric appliances has led to cash incentives. Various state or local agencies or utility companies (such as in California) offer rebates to new appliance purchasers proportional to the amount of energy saved by using the new appliance. This further increases the continuing demand and need for refrigerators and other appliances with increased efficiency.
As a result of the above considerations considerable research and effort has gone into the redesign of appliances, including components thereof such as motors, in order to increase electric efficiencies, and to meet present or anticipated environmental concerns, with regulations and goals aimed at reducing power consumption by as much as 30%.
Thus, it would be extremely desirable to provide an improved high efficiency fan motor for a household refrigerator which also could be used (with or without modification) as a refrigerant condenser fan motor.
Improved low power motors of the type we contemplate for use in refrigeration systems may advantageously be of the "brushless dc" or "electronically commutated motored" type. However, this type of motor can be damaged if the motor stalls, or ceases to attain desired operating speeds when first starting, or rotates at lower than normal speeds under load conditions. In the absence of a back emf or voltage associated with rotation of the rotor, the applied line voltage may cause excessive current flow through the motor windings which may exceed the rated current carrying capacity of the windings and lead to overheating and/or failure. Accordingly, it is desirable to provide adequate starting torque, and it is also highly desirable to provide means to detect motor stall, and to provide adequate restarting torque and/or current limiting in the event of motor stall.
Notwithstanding all of the above, in highly competitive markets such as, for example, the household refrigerator market it is also very important to keep the cost of improved motors to a minimum since many consumers are unwilling, or unable, to pay higher prices for energy saving improvements, notwithstanding the fact that initial costs often are recouped many times over the multiple year life of a machine. Thus, it is important that initial costs for improved products be minimized by providing a readily manufacturable design.
Also, notwithstanding all of the above, it is very important that motors for equipment having a long service life (e.g., household refrigerators) exhibit reliable operation and have a long life in view of consumer expectations and past experience with equipment that requires little or no maintenance for extended periods of continuous use. We have determined that brushless motors combined with solid state control device circuitry can provide the desired good reliability and low maintenance operation.